1. Field of the Invention
The subject invention is directed to a variable displacement vane pump, and more particularly, to a hydrostatically balanced multi-action variable displacement vane pump with variable cam timing, vane seals for reducing internal cross-bucket leakage, and floating face seals for reducing radial leakage.
2. Description of Related Art
Variable displacement vane pumps are well known in the art, and have been employed as fuel pumps in aircraft from many years. Most variable displacement vane pumps utilize a single lobe cam ring design, as disclosed for example in U.S. Pat. No. 5,545,014, 5,545,018 and 6,719,543, the disclosures of which are herein incorporated by reference in their entireties.
Typically, a circular cam member is employed about a relatively smaller circular rotor. Low pressure fluid is delivered to the rotor surface where the fluid is compressed within vane buckets. The compressed or high pressure fluid is then discharged through an outlet. When concentric, the pump provides zero or little fluid flow but when displaced to a position of maximum eccentricity, maximum fluid flow occurs. Under these conditions, large bearings are required to sustain the rotor reaction forces under high discharge pressure conditions. Further, these rotor reaction forces may disrupt or cause poor operation of the pump and/or poor operation of the system containing the pump.
For a variable displacement pump, it is desirable for the pump to be a balanced pump to mitigate the effects of the internal forces. Thus, many fixed displacement vane pumps use a balanced rotor arrangement, wherein bearing loads are eliminated by providing multiple lobes (e.g., two or even three lobes) on a cam ring. For example, see U.S. Pat. No. 4,272,227 and 6,478,559, the disclosures of which are herein incorporated by reference in their entireties. Such high-pressure vane pumps for aircraft applications and the like must be designed with cost, size, weight, complexity, performance and durability requirements in mind. In order to achieve the high performance requirements, efforts should be made to reduce possible internal leakage due to the low viscosity of the operation fluid, which is fuel.
In view of the above there is a need for an improved pump that is well-balanced, has improved vane assemblies, achieves better sealing and leakage control, and has parts which serve multiple functions to simplify design.
The subject invention is directed to a balanced variable displacement pump in the form of a pump cartridge that has a dual-action pumping element with an improved seal design to reduce internal cross-port leakage within the pumping element, and which also has a variable cam ring for selectively changing the effective displacement of the pump with a minimum amount of control torque. The benefits associated with the subject invention include high durability, high efficiency, easy displacement control, compact size and low cost.